A variety of robotic systems and end effectors have heretofore been devised for the grappling, handling and manipulation of diverse objects. For operations in the environment of outer space, the Shuttle Orbiter spacecraft has been equipped with a remote manipulating system for such purposes as maneuvering a payload from a spacecraft bay to a deployment position or for grappling a free-flying space satellite or other object. The system is subject to control by a human operator relying on visual observation or television viewing of the target object. For almost all such applications, the grappling device or end effector associated with the manipulator arm is desirably of small size, light weight, and readily adaptable to handling payloads of various sizes, masses, and shapes.
Previously, in space operations payloads have been attached to the arm of the remote manipulator system by a cable snare and tensioning grappling mechanism, often referred to as a Standard End Effector. The Standard End Effector requires a grapple fixture to be attached to the object to be grappled. Such a grapple fixture consists of a mounted post with three alignment cams arranged in equiangular spacing of 120 degrees surrounding the post. The disadvantages of the Standard End Effector include mechanical complexity and low reliability. Disadvantages associated with the grapple fixture used in conjunction therewith are its large physical envelope, precise tolerance requirements, and high manufacturing cost. Other end effectors have also been devised, such as disclosed in U.S. Pat. No. 4,921,292 which incorporate permanent magnets for using the attraction of magnetism to ferrous materials for attaching an object or payload. A significant disadvantage of a magnetic end effector with a permanent magnet is that if the mechanical linkage which actuates the magnet fails to function, then the attached object cannot be released. Additionally, since such an end effector requires a rigidized sensing grapple fixture for operation, should the end effector lose electrical power, the payload cannot be released by the remote manipulator system.